(a) Field of the invention
The invention relates to a color wheel with periodic color changes of light beam, and particularly to a color wheel producing original colors of light in a projection display device.
(b) Description of the Prior Art
In order to create color contrast in a projection display device, a color wheel is installed on the optical light path of a projection display device. Filter segments of various colors are installed on the periphery of the color wheel and are rotated around the central axis of the color wheel. By rotating filter segments on the color wheel, the filter segments are alternately inserted into the optical path and thereby the desired periodic color change is produced. Then the projection display device can adjust color contrast in coordination with light valve action.
FIG. 1 is a color wheel disclosed in U.S. Pat. No. 5,868,482. On a shaft 11 of a motor 10, a holding device 12 is used for fixing a carrier 13. On an outer edge area of the carrier 13, there is a recess 18 with a balancing device that serves to compensate imbalances during high speed rotation of the color wheel. On an inside edge area of the carrier 13, there is a ring recess 14 filled with adhesive. An adhesive film 16 on one end of each filter segments 15 is bonded to the ring recess 14 and can be accurately positioned radially and axially against the stop 19 on the inside edge area of the carrier 13. Therefore, the filter segments 15 form a continuous ring. A ring 17 that covers the ring recess 14 is mounted to the stop 19 for fastening the filter segments 15 to construct a color wheel. As a result, the color wheel moves the ring recess 14 away from the light beam projecting path to avoid deterioration of adhesive due to the heat of light.
However, because of consumer demand for lightness, thinness, shortness and smallness, projection display devices have been miniaturized, so is the color wheel becoming smaller and smaller. Therefore, when high temperature light beam impinges on the downsized filter segments 15, heat is rapidly conducted to the bonding ends of the filter segments 15 that are sealed on both sides and heat cannot be radiated resulting in rising temperature, so the adhesive becomes deteriorated because of the high temperature. Meanwhile, because one end of the filter segment 15 is coated with adhesive film 16 only on its one side to bond to the carrier 13, and the carrier 13 is subjected to projection of stray and deviated light caused by noises or alignment tolerances, resulting in rising temperature on the metal carrier 13 consequently to deterioration of the adhesive. Furthermore, another side of the filter segments 15 is in direct contact with the ring 17, and the adhesive has poor heat conduction much different than the heat conduction coefficient of the ring 17, so there is a temperature difference between two sides of the bonding end of filter segments 15, resulting in a thermal stress that causes the filter segments 15 to crack during high speed rotation. As a result, these defects degrade the quality of the product.
The objective of the invention is to provide a color wheel, by changing the position and size of a glued side of filter segment, and providing proper heat diffusing paths for the glued side, to prevent thermal stress and upgrade product quality.
Another objective of the invention is to provide a color wheel to avoid deterioration to the glue and upgrade product reliability by obstructing direct projection of light onto the glue and reserving clearances for heat insulation and diffuseness.
To achieve the above objectives, the invention has a motor with a rotating casing. Protruding from a center of an upper side of the rotating casing, there is a rotating shaft. One end of each fan-shaped filter segment is in contact with the rotating shaft, while one side of its lower surface is a formation of a glue area coated with glue, being glued onto the upper side of the motor, forming a rear clearance from the upper side, the sides of filter segments are joined to become a ring shape around the rotating shaft. The ring-shaped obstructing plate has a center hole that is mounted onto the rotating shaft, keeping a clearance from the filter segments, and there is a ring recess on the outside of the obstructing plate.